Along with the recent growth of the aging population, the number of cases of proximal femur fractures is increasing in the elderly, and bone fixation treatments with bone fixation apparatuses are widely performed. Since reduction at an early stage in bone fixation treatment and fixation methods have a huge effect on postoperative process, bone fixation apparatuses used for femoral neck fractures or femoral trochanter fractures with a firm fixing force are needed to maintain reduced position. A femur fixation apparatus disclosed in Patent Document 1 is an example of such bone fixation apparatuses.
FIGS. 17 and 18 show a femur fixation apparatus of Patent Document 1. This femur fixation apparatus 1A includes a lag screw (a femoral neck threaded rod part) 2A that is inserted into a bone including a femoral head of a fractured femur and an intramedullary nail (intramedullary rod part) 3A that is inserted with the lag screw 2A and inserted into a femoral shaft. An adjuster 4A is installed in the intramedullary nail 3A, and a stopper 40A formed to the lower end of the adjuster 4A engages with one of grooves 22A formed in the lag screw 2A, thereby preventing rotation of the lag screw 2A in its circumferential direction.
The adjuster 4A has a cylindrical part 8A threadedly engaged with an inner surface of the intramedullary nail 3A, a screw rotation part 9A supported to be rotatable in the circumferential direction but immovable up and down with respect to the cylindrical part 8A, and a sliding part (rotation prevention part) 10A threadedly engaged with the screw rotation part 9A. The sliding part 10A is unrotatable with respect to the intramedullary nail 3A. When a surgeon rotates the screw rotation part 9A with such operation tool as wrench, the sliding part 10A slides in an up-down direction relative to the intramedullary nail 3A. The stopper 40A is formed to the lower end of the sliding part 10A. Slide-moving the sliding part 10A downward engages the stopper 40A with the groove 22A of the lag screw 2A.
Also, an end cap 5A is mounted at the upper end of the intramedullary nail 3A. The end cap 5A has a male screw part 51A for threadedly engaging with a female screw part 81A of the cylindrical part 8A.
The femur fixation apparatus 1A further includes three rotation-prevention pins (femoral neck threaded rod auxiliary part) 61A and is configured to prevent a fractured segment from being dislocated in three-dimensional directions with the rotation-prevention pins 61A inserted into the femur and through the intramedullary nail 3A. Also, the sliding part 10A of the adjuster 4A is formed with an interference prevention hole and/or an interference prevention groove for preventing interference with the rotation-prevention pins 61A.
On the other hand, osteosynthesis devices disclosed in Patent Document 2 include a set screw fitted in an intramedullary nail and an end cap, and is configured to fix a lag screw in place with a protrusion formed to the end of the set screw and to fix a sub pin in place with a protrusion of the end cap inserted through the set screw. The set screw has a head part (a rotation part) with a fitting piece and a body part (a sliding part) formed with a fitting groove. The head part is pressed into the body part from a longitudinal direction of the body part with a specialized tool so that the fitting part of the head part is fitted into the fitting groove of the body part. As a result, the body part is attached to the head part so as to be freely rotatable but inseparable against certain force. Also, the head part of the set screw is formed with a slit penetrating from an inner peripheral surface to an outer peripheral surface. After the head part is fitted to the body part, the slit is slightly widened to enhance the resistance between the head part and a screw groove of the intramedullary nail.
Also, one way sliding devices for intertrochanteric fixation implants disclosed in Patent Document 3 are devices for treating fractures, including an intramedullary member sized and shaped for insertion along a longitudinal axis of a bone within a medullary canal thereof.